In the electronic keyboard system known as, for example, a synthesizer or an automatic player system, key sensor units are provided in association with the key board, and the key sensor units respectively detects key motions in the keyboard for deciding on the notes assigned to the depressed keys as well as the key touches. These notes and the key touches are used for producing sounds in the synthesizer, or are memorized in an information storage of the automatic player system for reproducing the sounds. The synthesizer is well known in the art, and the automatic player system is, by way of example, disclosed in U.S. Pat. No. 4,744,281.
Conventionally, the key sensor units were formed by mechanical switches, however, the mechanical switches are not fit for accurate sensing and use for a prolonged period of time due to the physical contacts. For this reason, the mechanical switches tend to be replaced with optical key sensors in the electric keyboard system, and the optical key sensors are becoming majority in the automatic player system.
In the electronic keyboard system, the optical key sensors are respectively associated with keys, and are coupled in parallel to a controller through wirings. Upon depressing a key, the key motion is detected by the associated optical key sensor, and the optical key sensor produces electric signals representative of the note assigned to the depressed key and the key touch. The electric signal is relayed to the controller, and the controller fetches the data represented by the electric signals for processing.
However, a problem is encountered in the prior art electronic keyboard system in complexity of the wiring arrangement. This is because of the fact that the optical key sensors are coupled in parallel to the controller through the private wirings. The complex wirings occupies a large amount of space, and difficulties are experienced in fitting the optical key sensors and the wirings, because of the limitation in the space available for the installation.
Moreover, the wirings tends to be close one another, and, for this reason, an electromagnetic field induced around the wirings is much liable to be influence on the electric signals. This results in undesirable destruction of the data on the electric signals.